Refactoring some actor messages into a wrapper object
Miniscule spacing fix
(Hopefully) improving archive-signing behavior

Before, the server waited until JNLPs and shim '.jar's were written out and signed before returning the JNLP URL.  Now, the JNLP URL is returned immediately, and JNLP/'.jar' writes are queued up through an actor to avoid disk thrashing and provide a more-responsive experience